INT-201:
Computer Network and
Communication System
Module1: Introduction
อ.ดร. ภัทร ลีลาพฤทธิ์
Computer Networking: A
Top Down Approach ,
4th edition.
Jim Kurose, Keith Ross
Addison-Wesley, July
2007.
Dr. Pattara Leelaprute
Computer Engineering Department
Kasetsart University
pattara.l@ku.ac.th
http://www.cpe.ku.ac.th/~pattara/int201
Introduction
1-1
Outline
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-2
Definition of Computer
 Devices for performing computations
at high speeds with great accuracy
 A machine that can be programmed to
manipulate symbols
 Physical components are known as
“Hardware”
Introduction
1-3
Where to find Computer?
 Home
 Business
 School
 Where else?
Hospital, automobiles, aircraft,
electronic appliance, mobile phone, etc…
Introduction
1-4
Computer Systems
 Hardware (HW)
 Actual
physical machines (equipment)
that make up the computer (e.g. monitor,
keyboard)
 Software (SW)
 Programs
written for a specific
application are often called software
(e.g. Window XP, Linux, Microsoft word)
Introduction
1-5
Computer Categories
 Personal Computer
 Desktop Computer
 Notebook
 PDA – Personal Digital Assistant
 Supercomputer  Mainframe
 High Computation Power
 Server
 Workstation
Introduction
1-6
Server & Workstation
Introduction
1-7
Computer Components
 Input Devices
 Output Devices
 Computing & Processing Unit
Introduction
1-8
Computer Components (details)
Input Devices
CPU
Secondary
Memory
(DVD,
FDD,
HDD)
Main
Memory
Output Devices
HD
*CPU= Central Processing Unit
Introduction
1-9
Computer Components (pictures)
Hard disc
CPU
Introduction
1-10
Computer Memory
Can be divided into 2 Categories
RAM (Random Access Memory)
 ROM (Read Only Memory)

 Memory in Computer
 Main Memory
 Secondary Memory
Introduction
1-11
Main Memory VS Secondary Memory
 Main Memory
 Much
 Secondary Memory
faster
 More expensive
 Volatile (Temporary)
 Slower
 Less
expensive
 Permanent
Introduction
1-12
1. Main Memory
 Memory Cell -> Byte -> bit
 1 Byte = 8 bits
Introduction
1-13
2. Secondary Memory
 Floppy disk
 Hard disk
 CD-ROM, CD-R, CD-RW
 DVD-ROM, DVD-R, DVD-RW
 Blu-ray disc
Etc…
Introduction
1-14
Data Representation
 Data in computer is represented in “bit”
 bit = binary digit
• 0 or 1


Byte = 8 bits
1 byte can represent many kids of data
• 1 byte = 011000012
• the above 1 byte means, 97 or “a” in ASCII code
• ASCII =American Standard Code for Information Interchange.
• the meaning of 1 byte depends on the program
• Photos, Voice, Video, etc
1 Kbyte = 210 = 1024 bytes (KB)
1 Mbyte = 220 = 1,048,576 bytes (MB)
1 Gbyte = 230 = 1,073,741,824 bytes (GB)
1 Tbyte = 240 = 1,099,511,627,776 bytes (TB)
Introduction
1-15
ASCII code
 8bit code for character
representation
(7 bits plus parity)
 0-127 represents the
letter of alphabet,
numbers and symbols
Introduction
1-16
Binary and Decimal
 How to convert binary to decimal?
1 0 0 1 1
2
2 5 5 1
10
1 0 0 1 1
1 0 0 1 1
= ?
= ?2x103 + 5x102 + 5x101 + 1x100
2
= 1x24 + 0x23 + 0x22 + 1x21 + 1x20
2
= 24 + 21 + 1 = 16+2+1 = 19
How to convert decimal to binary ?
Introduction
1-17
Boolean Expression
 And
 Or
 Not
0
0
1
1
and
and
and
and
0
1
0
1
0
0
1
1
or
or
or
or
=
=
=
=
0
1
0
1
=
=
=
=
0
0
0
1
0
1
1
1
not 0 = 1
not 1 = 0
Introduction
1-18
Type of Application
 Local application
 Program, such as a word processor, that is
stored on the hard disk of the computer.
 The application runs only on that computer.
 Network application
 Program that is designed to run over a network,
such as the Internet.
 A network application has two components, one
that runs on the local computer and one that
runs on a remote computer.
 ex., Email
Introduction
1-19
Outline
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-20
Operating System (OS)
 Software component of a computer system
 Responsible for the management and
coordination of activities and the sharing of
the resources of the computer.
 All computerized devices, such as servers,
desktops, laptops require an OS
 ex. Microsoft Windows, MAC OS X, Linux,
Unix
Ex., RAM, Hard disk, CPU
Introduction
1-21
Operating System (OS)
 What does OS do?
 Program execution
 Memory management
 Multitasking
 Disk access and file systems
 Device drivers (printer, monitor)
 Input/Output
 Networking
 Let’s think about WORD application.
 Write a report and print it out.
• OS collaborates keyboard, monitor, hard disk, and printer.
Introduction
1-22
User Interface (for OS)
 Command line interface (CLI)
 Graphical user interface (GUI)
CLI
Introduction
1-23
Quiz
 ((1 and 0) or (1 and 1)) = ?
 What is I/O device ?
 What is RAM and ROM ?
 1 byte = xxx bits
 1 Mbyte = xxx byte
 10000102 = ?
Introduction
1-24
Outline
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-25
What’s the Internet: overview
PC
 millions of connected
computing devices:
hosts = end systems
wireless
laptop
 running network
cellular
handheld
apps
 communication links
 fiber, copper,
access
points
radio, satellite
wired
links
 transmission
rate = bandwidth
 routers: forward
router
packets (chunks of
data)
Mobile network
server
Global ISP
Home network
Regional ISP
Institutional network
Introduction
1-26
“Cool” internet appliances
Web-enabled toaster +
weather forecaster
IP picture frame
http://www.ceiva.com/
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
Internet phones
Introduction
1-27
What’s the Internet: “nuts and bolts” view
 protocols control sending,
Mobile network
receiving of msgs

e.g., TCP, IP, HTTP, Skype,
Ethernet
 Internet: “network of
networks”


loosely hierarchical
public Internet versus
private intranet
Global ISP
Home network
Regional ISP
Institutional network
 Internet standards
 RFC: Request for comments
 IETF: Internet Engineering
Task Force
Introduction
1-28
What’s the Internet: a service view
 communication
infrastructure enables
distributed applications:
 Web, VoIP, email, games,
e-commerce, file sharing
 communication services
provided to apps:
 reliable data delivery
from source to
destination
 “best effort” (unreliable)
data delivery
Introduction
1-29
What’s a protocol?
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
 machines rather than
humans
 all communication
activity in Internet
governed by protocols
protocols define format,
order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt
Introduction
1-30
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
Introduction
1-31
Outline
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-32
Network structure:
 network edge:
applications and
hosts (send-receive msg)
 access networks,
physical media:
wired, wireless
communication links
 network core:
 interconnected
routers
 network of
networks
Introduction
1-33
The network edge:
 end systems (hosts):



run application programs
e.g. Web, email
at “edge of network”
peer-peer
 client/server model


client host requests, receives
service from always-on server
client/server
e.g. Web browser/server;
email client/server
 peer-peer model:


minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrenth
Introduction
1-34
Network edge: reliable data transfer
service
Goal: data transfer
between end systems
 handshaking: setup
(prepare for) data
transfer ahead of time


Hello, hello back human
protocol
set up “state” in two
communicating hosts
 TCP - Transmission
Control Protocol

Internet’s reliable data
transfer service
TCP service [RFC 793]
 reliable, in-order byte-
stream data transfer

loss: acknowledgements
and retransmissions
 flow control:
 sender won’t overwhelm
receiver
 congestion control:
 senders “slow down sending
rate” when network
congested
Introduction
1-35
Network edge: best effort (unreliable)
data transfer service
Goal: data transfer
between end systems

same as before!
 UDP - User Datagram
Protocol [RFC 768]:
 connectionless
 unreliable data
transfer
 no flow control
 no congestion control
App’s using TCP:
 HTTP (Web), FTP (file
transfer), Telnet
(remote login), SMTP
(email)
App’s using UDP:
 streaming media,
teleconferencing, DNS,
Internet telephony
Introduction
1-36
Access networks and physical media
Q: How to connect end
systems to edge router?
 residential access nets
 institutional access
networks (school,
company)
 mobile access networks
Keep in mind:
 bandwidth (bits per
second) of access
network?
 shared or dedicated?
Introduction
1-37
Residential access: point to point access
 Dialup via modem
up to 56Kbps direct access to
router (often less)
 Can’t surf and phone at same
time: can’t be “always on”

 DSL: digital subscriber line
deployment: telephone company (typically)
 up to 1 Mbps upstream (today typically < 256 kbps)
 up to 8 Mbps downstream (today typically < 1 Mbps)
 dedicated physical line to telephone central office

Introduction
1-38
Residential access: cable modems
 HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream, 2
Mbps upstream
 network of cable and fiber attaches homes to
ISP router
 homes share access to router
 deployment: available via cable TV companies

Introduction
1-39
Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Introduction
1-40
Company access: local area networks
 company/univ local area
network (LAN) connects
end system to edge router
 Ethernet:
 10 Mbs, 100Mbps,
1Gbps, 10Gbps Ethernet
 modern configuration:
end systems connect
into Ethernet switch
 LANs: chapter 5
Introduction
1-41
Wireless access networks
 shared wireless access
network connects end system
to router

via base station aka “access
point”
 wireless LANs:
 802.11b/g (WiFi): 11 or 54 Mbps
 wider-area wireless access
 provided by telco operator
 ~1Mbps over cellular system
(EVDO, HSDPA)
 next up (?): WiMAX (10’s Mbps)
over wide area
router
base
station
mobile
hosts
Introduction
1-42
Home networks
Typical home network components:
 DSL or cable modem
 router/firewall/NAT
 Ethernet
 wireless access
point
to/from
cable
headend
cable
modem
router/
firewall
Ethernet
wireless
laptops
wireless
access
point
Introduction
1-43
Physical Media
 Bit: propagates between
transmitter/rcvr pairs
 physical link: what lies
between transmitter &
receiver
 guided media:

signals propagate in solid
media: copper, fiber, coax
Twisted Pair (TP)
 two insulated copper
wires


Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5:
100Mbps Ethernet
 unguided media:
 signals propagate freely,
e.g., radio
Introduction
1-44
Physical Media: coax, fiber
Coaxial cable:
Fiber optic cable:
conductors
 bidirectional
 baseband:
pulses, each pulse a bit
 high-speed operation:
 two concentric copper


single channel on cable
legacy Ethernet
 broadband:
 multiple channels on
cable
 HFC
 glass fiber carrying light

high-speed point-to-point
transmission (e.g., 10’s100’s Gps)
 low error rate: repeaters
spaced far apart ; immune
to electromagnetic noise
Introduction
1-45
Physical media: radio
 signal carried in
electromagnetic
spectrum
 no physical “wire”
 bidirectional
 propagation
environment effects:



reflection
obstruction by objects
interference
Radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., Wifi)
 11Mbps, 54 Mbps
 wide-area (e.g., cellular)
 3G cellular: ~ 1 Mbps
 satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
Introduction
1-46
Outline
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-47
The Network Core
 mesh of interconnected
routers
 the fundamental
question: how is data
transferred through net?
 circuit switching:
dedicated circuit per
call: telephone net
 packet-switching: data
sent thru net in
discrete “chunks”
Introduction
1-48
Network Core: Circuit Switching
End-end resources
reserved for “call”
 link bandwidth, switch
capacity
 dedicated resources:
no sharing
 circuit-like
(guaranteed)
performance
 call setup required
Introduction
1-49
Network Core: Circuit Switching
network resources
(e.g., bandwidth)
divided into “pieces”
 pieces allocated to calls
 dividing link bandwidth
into “pieces”
 frequency division
 time division
 resource piece idle if
not used by owning call
(no sharing)
Introduction
1-50
Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
Introduction
1-51
Network Core: Packet Switching
each end-end data stream
divided into packets
 user A, B packets share
network resources
 each packet uses full link
bandwidth
 resources used as needed
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
resource contention:
 aggregate resource
demand can exceed
amount available
 congestion: packets
queue, wait for link use
 store and forward:
packets move one hop
at a time

Node receives complete
packet before forwarding
Introduction
1-52
Packet Switching: Statistical Multiplexing
100 Mb/s
Ethernet
A
B
statistical multiplexing
C
1.5 Mb/s
queue of packets
waiting for output
link
D
E
Sequence of A & B packets does not have fixed pattern,
bandwidth shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
Introduction
1-53
Packet-switching: store-and-forward
L
R
 takes L/R seconds to
R
transmit (push out)
packet of L bits on to
link at R bps
 store and forward:
entire packet must
arrive at router before
it can be transmitted
on next link
 delay = 3L/R (assuming
zero propagation delay)
R
Example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 transmission delay = 15
sec
more on delay shortly …
Introduction
1-54
Packet switching versus circuit switching
Packet switching allows more users to use network!
 1 Mb/s link
 each user:
 100 kb/s when “active”
 active 10% of time
 circuit-switching:
 10 users
 packet switching:
 with 35 users,
probability > 10 active
at same time is less
than .0004
N users
1 Mbps link
Q: how did we get value 0.0004?
Introduction
1-55
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
 great for bursty data
resource sharing
 simpler, no call setup
 excessive congestion: packet delay and loss
 protocols needed for reliable data transfer,
congestion control
 Q: How to provide circuit-like behavior?
 bandwidth guarantees needed for audio/video apps
 still an unsolved problem (chapter 7)

Q: human analogies of reserved resources (circuit
switching) versus on-demand allocation (packet-switching)?
Introduction
1-56
Summary
 Introduction to Computer
 Operating System
 What is Internet?
 Network structure
 The Network Core
Introduction
1-57
Tips (useful links)
 http://en.wikipedia.org
 http://th.wikipedia.org/wiki/
 http://longdo.com
 http://cisco.netacad.net
Introduction
1-58
Tips (Programming Languages)
 Program
 A set of instructions for a computer to
follow, written in specific programming
language
 Types of programming language
 High-Level Language
 Machine Language
 Assembly Language
Introduction
1-59
Tips (Programming Languages)
 High-level Language
 Nearly like human word
SUM := A * 2 + ALPHA/3;
 Assembly Language
 Some key words are understandable
MULL3 A, #2, R
ADDL3R6, R7, SUM
 Machine Language
 Only “0” and “1”
00011000011
00011001111
10011000111
Computer itself understands only Machine language
Introduction
1-60
Tips (Programming Languages)
High-Level Languages
 Procedural Language
 Fortran
 Cobol
 Basic
 C
 Pascal
 Object-Oriented Language
 C++
 C#
 Java
 Functional Language
 Lisp
 Logic Language
 Prolog
Introduction
1-61
Homework
 What is Blu-ray disc? (~1000 characters)
 Give 3 names of the application, describe
what does it do and its type. (~1000 characters)
 Describe why the service in the Internet is called
best effort service? (~1000 characters)
 Describe how to represent the picture that has the
size of X*Y pixel, and has 8 tone level (0~7) for each
R,G,B color by using binary. In addition, calculate
the number of bit needed for that X*Y picture.
• Please write your name, student ID, hand in date on the top.
• Deadline is 11th June 2008 (next class).
Introduction
1-62